This may only be useful for low-FOV players like myself, but I 'discovered' a way to dynamically change your FOV while playing, by holding down a button.
This is by taking advantage of the change to your FOV that happens when you use the scope. Of course this might not be useful for people that use the scope for its original purpose regularly, and the scope crosshair is still overlayed on the screen, but I thought it useful enough to point out anyway.

As you'll see, the first selected FOV is modified to 145- I couldn't really play like this but it gives a relatively massive view of the map for as long as you hold down the button. You can change this value to any FOV you want. The magnification level is also set to 0, so it doesn't zoom in. The other zoom levels function like they normally would- however, if you want to switch between 2 or 3 different FOVs, you can amend the relevant lines in the same way.